According to the standard design, known wind-power plants comprise a tower at whose upper end a generator is mounted in a generator housing. A rotor is connected to the generator, either directly or by a gearbox, and typically carries three rotor blades. So as to adjust the positions of the rotor blades to different wind speeds, the blades are each connected to the rotor for pivoting about a respective longitudinal blade axis. Large diameter axial-radial roller bearings used for this purpose in practical experience are accordingly referred to as pitch bearings. The task of these bearings and of a controller is to adapt the pitch of the rotor blades to the current wind speed or to the operating state of the system. In practice, double-row four-point ball bearings are frequently used for this purpose, such as those described in DE 20 2006 008 288 [US 2010/0322543] and WO 2009/147865 [US 2010/0085756], for example. Double-row four-point ball bearings can be manufactured comparatively cost-effectively, are quite compact, and can transfer high torques.
While in the known wind-power plants generally only the pitch of the blades is varied when the wind speed changes significantly, it is now considered desirable to vary the pitch more frequently than before, and in particular synchronously with the rotor speed, so that much higher permanent loads result for the pitch bearings. For this reason axial-radial roller bearings are required that have increased load-bearing capacity and durability with small size. In this context it must be taken into consideration that, under the wind load, very large tilting moments act on the pitch bearing because of the considerable lengths of the rotor blades that in particular axially strain the roller bearings.
Axial-radial roller bearings having the characteristics described above are known from WO 2007/003866 (FIG. 10) [U.S. Pat. No. 8,047,792], DE 20 2005 026 141 and DE 10 2008 009 740 [US 2011/0115233], wherein the axial-radial roller bearings described each have a three-row design with two axial roller bearings set at an axial spacing from each other and an interposed radial roller bearing. So as to be able to absorb the high tilting moments that occur with use as pitch bearings, the rolling elements of the axial roller bearings must have sufficient dimensions.